1. Field of the Invention
This invention relates to carburetors and more particularly to carburetors used in emission controlled motor vehicle engines.
2. Description of the Prior Art
In conventional carburetors an outer vent is provided in the carburetor float chamber to prevent the fuel vapor generated inside the float chamber from being emitted into the atmosphere. This outer vent is connected with a charcoal canister by a fuel vapor line. The fuel vapor generated inside the carburetor float is adsorbed by the charcoal canister. The fuel adsorbed by the charcoal canister is then sent to the engine via a purge port provided in the air intake and is burned. In this case, the fuel vapor line is closed while the engine is running and is open whenever the engine is shut down.
Such conventional fuel vapor control devices suffer from a drawback in that the starting performance of the engine deteriorates after the engine has been shut down for a time longer than a given period. Specifically, the starting performance deteriorates due to the fact that the fuel vapor which aids in the starting of the engine and which is normally stored in the intake system (i.e. the intake manifold, carburetor float chamber, air cleaner, etc.,) is adsorbed by the charcoal canister when the engine is off. Furthermore, the usual type of charcoal canister also adsorbs fuel vapor from the fuel tank. The canister is connected with the fuel tank and the fuel vapor generated by the warming of the fuel tank while the vehicle is stopped is temporarily stored in the charcoal canister. However, when the fuel vapor line connecting the carburetor float chamber with the charcoal canister is open, there is a danger that a portion of the fuel vapor in the fuel tank will escape through the charcoal canister and be emitted into the atmosphere via the carburetor float chamber, air intake and air cleaner.
Accordingly it is the object of the present invention to eliminate the previously mentioned conventional drawbacks.